Significance While the majority of the air in most urban areas contains a large array of particles, there is little information concerning the degree of their toxicity either as mixtures or individual particles. Objectives The present studies were designed to test the toxic effects of two classes of pollutant particle mixtures on the lungs of nonhuman primates. One of these particle mixtures which is ubiquitous in much indoor air, environmental tobacco smoke, will be tested for effects on postnatal lung development in neonatal rhesus monkeys. The other, a mixture of carbon black and ammonium nitrate, will be tested for effects on the respiratory bronchiole of adult rhesus monkeys. Results Our preliminary studies with fluorescent particles have established that the distribution of particulates within the respiratory system of nonhuman primates differs markedly from that which has been observed in other model species, especially rats and mice. The result of this study to date has been the development of new three-dimensional methods employing confocal microscopy to evaluate the distribution of these particles. Future Directions Exposures of neonatal rhesus monkeys to environmental tobacco smoke are underway. Exposure to carbon particles will begin within the next six months. KEYWORDS tobacco smoke, lung development, particles, toxicity FUNDING U.S. EPA Grant R8826246; UC Tobacco Related Res. Prog. Grant 7RT-011